The invention relates to polyesters which contain unbranched and/or branched alkyl side chains bound to the main chain by ester and/or ether bridges, and can be used in coatings or adhesives.
U.S. Pat. No. 3,375,540 discloses polyesters which are solid at room temperature and contain alkyl or alkylene side chains of substituted succinic acid anhydride, wherein the side chain is bound to the main chain by a carbon atom. Their melting points are only slightly lower than those of polyesters without such alkyl side chains.
Other polyesters contain side chains, formed from moieties of dimeric and trimeric fatty acids. The so-called dimeric fatty acids are formed by the condensation of unsaturated fatty acids and always contain trimeric fatty acid and monomeric fatty acids. The structure of the dimeric fatty acid has 2 carboxyl groups at the end of carbon chains and 2 additional carbon chains on a cyclohexene ring, double bonds being contained in the cyclohexene ring and in one chain. Trimeric fatty acids are formed by the reaction of an additional molecule of unsaturated fatty acid with a double bond of the cyclohexene ring and therefore they have the character of greatly branched unsaturated tricarboxylic acids. Such polyesters, due to the great branching of the main chain, have substantially elevated melt viscosities and, due to unsaturated groups, an undesirable reactivity and poor stability against light and oxidation.
Coatings of aminoplastic resins and polyurethanes having contents of such polyesters according to U.S. Pat. No. 4,423,179 and German OS No. 34 01 559 can be applied only from solution. Also, if, according to this German OS, monocarboxylic acids are esterified with them, low setting points* and viscosities do not result on account of the great chain branching. Also the polyesters prepared according to German OS No. 24 41 921 and 25 07 985 are not low-melting and require solvents in their fabrication, while a narrow molecular weight distribution and heavy branching of the polyesters are just as undesirable as the method of preparation by producing carboxyl polyesters and reacting them with epoxy alcohols or alkylene oxides. FNT *The expression "setting point" is used in the meaning of "glass transition temperature (Tg)", as more closely defined by the monography; Hans-Georg Elias "Makromolek/u/ le" H/u/ thig und Werf-Verlag, Basel/Heidelberg (1971) ISBN3-7785-0211-5, pages 310 to 313.
The known polyesters for the production of coatings and/or adhesives have excessively high melt viscosities with, in some cases, high molecular weights, and excessively high setting points. It is therefore difficult or impossible to process these polyesters or crosslinkable products made from them by reaction with functionalizing compounds, so as to be free of solvents or to have a low solvent content.
The problem therefore was to develop polyesters which, after a crosslinking, i.e., after reaction with functionalizing compounds and the crosslinking of the products thus obtained, will result in very elastic materials and will be able to be applied as films between room temperature and 50.degree. C. fabricated solvent-free or with little solvent. For this purpose it was necessary to lower the softening point below the polyesters corresponding to the state of the art, while at the same time preserving the molecular weight, to such an extent that polyesters liquid at room temperature and fluid functionalized polyesters will be obtained.
At the same time it was desired to strive for a low setting point in order to avoid embrittlement of the coatings and/or adhesives even at low temperatures.
The low setting point was to be sought after not only for polyesters with contents of aliphatic dicarboxylic acids, but also for predominant contents of aromatic polycarboxylic acids, which are often to be preferred as components, but which in the state of the art do not make low setting points possible.